You can specify custom Axis Items Labels by either specifying a XCategory or by manually setting TickPoint's labels.

XCategory is used when the data is not sequential, i.e. values on the X Axis have no meaning, for examle when the chart presents information for different companies (whose names are placed on the X axis) or other entities. In case X value is present in the data, and something else should be placed on the X axis, you need to go through the RadChart.DefaultView.ChartArea.AxisX.TickPoints collection and set Label for each TickPoint. Since the XCategory is already described in another help article - Categorical Charts this topic will demonstrate the second approach: